Fall-arrest systems with yielding mounting bracket for inspection purposes

ABSTRACT

A personnel fall-arrest system including a flexible safety track (1) which is anchored in spaced relation to a fixture (2) by track anchors (4), and a coupling component (7) for connecting a worker&#39;s safety harness to the track via a safety line (8), the component (7) being freely displaceable along the track. Each of the track anchors (4) is formed so that it becomes permanently deformed if subjected to heavy loading due to a fall, thereby signalling that the system requires to be checked and re-certified before further use.

This invention relates to a personnel fall-arrest system comprising aflexible safety track which is anchored in spaced relation to a fixtureby track anchors located at intervals along the track, and a couplingcomponent for connecting a worker's safety harness to said track via asafety line, said component being coupled to said track but being freelydisplaceable therealong.

The flexible safety track of a system of the kind to which the inventionrelates can most suitably be a metal cable which is threaded throughtrack-receiving eyes or sleeves provided on the track anchors. Suchanchors and the coupling component can be formed so that displacement ofthe coupling component along the track is not obstructed by the anchors(see e.g. United Kingdom Patent No 2 199 880).

Such systems serve to protect workers in situations where they wouldotherwise be exposed to risk of serious injury or death by falling. Forexample, they can be used for protecting workers on walkways runningalong the exteriors of structures, high above the ground, or on walkwaysabove open vats or other containers holding harmful liquids.Shock-absorbing means is normally incorporated in or associated withsuch systems for avoiding such abrupt arrest of a fall as could itselfcause serious injury.

Each of the components of a personnel fall-arrest safety system shouldbe capable, with a wide margin of safety, of sustaining the forces whichmay be imposed on it in the event of the fall of a person connected tothe coupling component. The track anchors must of course hold to thefixture. And they must also resist separation of the track from theanchors under the applied load.

Any personnel fall-arrest system should be systematically examinedperiodically in order to check that its components have not becomedamaged and are in serviceable condition. In the event that a fall takesplace, it is important that the system be thoroughly checked and thatany damaged parts be replaced before the system is again put to use.Such examinations are very demanding tasks, particularly in the case ofsystems of considerable length and systems in which important componentsare not conveniently placed for close inspection. The examinations haveto be carried out in situ, where there is an inherent risk of personalaccident. The work should be carried out by trained inspectors butdespite every care there is always the possibility of a defect beingoverlooked.

The present invention provides a system wherein there is means whichreduces the risk that impairment of the system, caused by heavy loadingdue to a fall, may be overlooked.

According to the present invention, there is provided a personnelfall-arrest system comprising a flexible safety track which is anchoredin spaced relation to a fixture by track anchors located at intervalsalong the track, and a coupling component for connecting a worker'ssafety harness to said track via a safety line, said component beingcoupled to said track but being freely displaceable therealong,characterised in that each of the anchors has an ultimate tensilestrength more than sufficient to prevent release of the track under thegreatest load liable to be imposed on said anchor due to the fall of aperson using the system, but is constructed so that under a loadsubstantially smaller than that maximum it will undergo a permanentdeformation which is apparent to the eye.

The invention departs from the common perception that the safety trackanchors in this kind of system should be robust enough to sustain a fullrange of fall-arrest loads without damage. Anchors of a system accordingto the invention are intentionally liable to be damaged if a personusing the system falls and the fall subjects the anchors to forces abovea certain magnitude. Because of the adequacy of the ultimate strength ofthe anchors, this liability of the anchors to become damaged does notmake the system unsafe. And the anchor damage, if it occurs, serves thevaluable purpose of making it obvious that the system has been subjectedto heavy stress and that repair work must be done before the system canbe certified for re-use.

Generally speaking, a large proportion of the load imposed on arrest ofa person during free fall will be transmitted from the safety track tothe fixture via the track anchors nearest the position where the falltakes place. The occurrence of anchor damage in a system according tothe invention can therefore make it apparent not only that the systemhas been subjected to heavy loading due to a fall but also at whichregion along the system the fall took place. If a worker falls andhangs, suspended from the safety track, immediate rescue of the workertakes precedence over other considerations. With a system as used priorto the present invention, even if steps are taken, following a fall, towarn against further use of the system until it has been re-certified asin good order, it is possible for the system to be left, after therescue operation, without any record of the actual place along thesystem where the fall occurred. Knowledge of where the system has beenmost heavily loaded does not relieve an inspectorate of responsibilityfor checking the entire system but it does ensure that the most heavilystressed part of the system will receive particuarly careful attention.

The occurrence of an obvious plastic deformation of an anchor under agiven load can be ensured by appropriate choice of the material used inthe construction of the anchor and of its form and dimensions.

As explained above, anchor damage in a system according to the inventionserves as an inspectorate alert signal. The resistance of the trackanchors to change of physical form under load determines the responsethreshold or "sensitivity" of the signal.

The resistance to deformation which the anchors of any given systemshould have, depends in part on the maximum load to which they may besubjected in the event of the fall of a person using the system. Thatmaximum load depends of course on the specifications of the fall-arrestsystem as a whole, including whatever shock-absorbing properties it mayhave. The said resistance must be low enough to ensure that anyindividual anchor will yield, by deformation, under a load substantiallysmaller than that maximum. The said resistance also depends on therequired signal sensitivity. It is not necessary and generally speakingit is not practical for the deformation resistance of the anchors to beso low that an anchor will become deformed by any load, however small,imposed in consequence of a fall, or a stumble, of a person using thesystem. It will normally suffice for the response threshold to be suchthat permanent deformation only occurs if the system is subjected toloading forces which would otherwise entail a real risk of some part orparts of the system sustaining damage without inducing any obviouswarning sign that such damage may have occurred.

It is preferable for individual anchors to undergo readily perceivablepermanent deformation when subjected to a load of 5 KN or less in aYield Test as follows:

Yield Test

The anchor to be tested is secured to a fixture in the same way as itwould be if it were used as intended in an actual fall-arrest system. Atraction force is applied to the track-receiving portion of the anchorby a traction machine working at an extension rate of 0.5 inches (1.27cm) per minute. The direction in which that force is applied in relationto the orientation of the anchor is such as to simulate the action of aforce exerted vertically downwardly on that portion of the anchor whenthe anchor is in its intended anchored orientation in an actualfall-arrest system. The distance, measured in the direction in which theforce is applied, by which the said track-receiving portion of theanchor is displaced from its original position in consequence of theapplication of a given force, as indicated on the machine gauge, is ameasure of the extent of deformation which the anchor undergoes underthat force.

A yield resistance of 5 KN as measured by the foregoing Yield Test isnot an absolute maximum. It is put forward as a practical upper limit.The safety track anchors can have a yield resistance of that relativelyhigh value in the case of a system in which the anchors are likely to besubjected to loading forces substantially in excess of 5 KN in the eventof the arrest of a free fall. In general however it preferable for thesafety track anchors of any system according to the invention to have ayield resistance below that value.

In preferred embodiments of the invention, the yield resistance ofindividual anchors in the system, as determined by the foregoing YieldTest, is such that the extent of permanent deformation, measured interms of the specified displacement of the track-receiving portion ofthe anchor, is at least 2 cm under a force of 3 KN. Observance of thiscondition is likely to ensure that any deformation of an anchor causedby the imposition of fall-arrest forces on the system in the vicinity ofan anchor will be very obvious.

In certain embodiments of the invention, each anchor is constructed sothat in a Yield Test as hereinbefore specified, it will undergo apparentpermanent deformation under a traction force which is less than 60% ofthe maximum load to which the anchor is liable to be subjected (due to afall) during use of the system in which the anchor is incorporated. Itis also recommended that each anchor be constructed so that in a saidYield Test it undergoes a said apparent permanent deformation under atraction force in the range of 2.5 to 4.5% of the ultimate tensilestrength of the anchor.

The occurrence of permanent plastic deformation of an anchor impliesthat the anchor has also contributed to shock-absorption. That is afurther advantage of a system incorporating anchors which yield in thatmanner.

It is recommended to use anchors each of which is constructed so thatmaterial of the anchor between the fixture and the safety track formsone or more loops or coils. The adoption of such a looped or coiledgeometric form facilitates realisation of a high ultimate tensilestrength in combination with a relatively low resistance to permanentplastic deformation.

A particularly advantageous form of anchor is one comprising (i) abracket having a head portion which surrounds and locates the safetytrack, a body portion formed by a loop of material between that headportion and the fixture, and a neck portion joining said head and bodyportions; and (ii) fastening means securing the body portion of thebracket to the fixture. Such a bracket can advantageously be constructedso that if it is subjected to progressively increasing traction in aYield Test as hereinbefore described, the bracket becomes deformed,before rupture thereof, into a condition in which the material whichpreviously formed the head, neck and body portions of the bracket formparts of a single loop. It is particularly beneficial for the saidmaterial between the fixture and the safety track to form a polygonalloop by which the anchor is secured to the fixture, and a neck portionprojecting from one corner of the polygon. Such a geometric form canconfer very desirable performance properties on the anchor. The head,neck and body portions of the bracket are preferably integral parts of asingle strip of material which has been folded about transverse axes todefine those bracket portions and so that two portions of the strip lieface to face to form a two-ply bracket wall in the region where thebracket body is secured against the fixture by the fastening means.

Each of the safety track anchors preferably comprises an anchor bracketand a single fastener about which the bracket will bodily pivot if asufficiently large turning moment is imposed on it in consequence ofheavy loading of the track at a position on one side of the anchor. If aportion of the safety track between two anchors is pulled downwardly andsubjected to heavy loading as a result of a fall, the forces transmittedto those two anchors can cause the two brackets to pivot about theirfasteners so that the forces on the head portions of the brackets andthe stresses on the contacting portions of the safety track are betterdistributed.

Certain embodiments of the invention, selected by way of example, willnow be described with reference to the accompanying drawings in which:

FIG. 1 shows part of a personnel fall-arrest system according to theinvention;

FIG. 2 shows a part of the system at the moment of a fall-arrest;

FIG. 3 is a side sectional elevation of part of an anchor bracket usedin that system;

FIG. 4 is a front elevation of that bracket;

FIG. 5 is a perspective view of that bracket and co-operating parts ofthe system;

FIG. 6 shows alternative fixing positions of such a bracket in relationto a walkway;

FIGS. 7a and 7b shows stages in the deformation of such a bracket underload;

FIG. 8 shows an alternative form of anchor bracket;

FIG. 9 is an end elevation of another form of safety track anchor;

FIG. 10 is a front elevation of a part of that anchor;

FIG. 11 shows an anchor as represented in FIGS. 9 and 10 at a stageduring its progressive deformation under load; and

FIG. 12 is a perspective view of part of a system according to theinvention in which the track anchors incorporate brackets of a moresimple form.

In the fall-arrest system represented in FIGS. 1 and 2, a safety trackin the form of a wire cable 1 is anchored to the underside of astructure 2 overhanging a worker's walkway 3. The cable can follow anendless course around the structure or it may extend between stations atwhich the ends of the cable are secured to the fixture via suitable endfittings on the cable. Cable anchors 4 located at intervals along thelength the cable serve to support the cable and anchor it to thestructure 2. Each of the anchors 4 comprises a cable-supporting andlocating bracket 5 and a fastening bolt 6 which secures the bracket tothe fixture 2.

A coupling component 7 is threaded onto the cable 1 and is freelyslidable therealong. A worker's safety harness is connected to thatcoupling component via a lanyard 8.

The construction of the brackets 5 is shown in FIGS. 3 and 4. Eachbracket has a body portion 9 in the form of a quadrilateral loop, a headportion 10 of tubular form and a neck 11 joining the head and bodyportions. The bracket is formed from a single strip of metal by bendingthe strip about transverse axes. Opposed end portions of the stripoverlap to give two sides 12, 13 of the quadrilateral body portion ofthickness twice that of the strip. The overlapping end portions of thestrip are spot-welded together in each of the sides 12, 13. Holes 14, 15are formed in the body sides 12, 13 respectively for the reception andlocation of a fastening bolt 6 (FIG. 2). When the anchor is installed,the bracket is secured to the fixture by only one bolt. The bracket canbe orientated with either body side 12 or body side 13 against thefixture and it is for that reason that each of those sides is formedwith a hole for an anchor bolt. Larger holes 16, 17 are formed in thebody sides opposite sides 12 and 13 to allow access of a tool to thehead of the bolt.

In the installed system, the cable 1 passes through the tubular headportions 10 of the anchor brackets 5. The cable can slide axially withinthe head portion of each bracket. It is beneficial to fit the tubularhead portion of each bracket, as shown in FIGS. 2 and 5, with a flexibleextension tube 18 which projects from each side of such head portion. Itis very suitable for such extension tube to be of synthetic polymericmaterial, e.g. nylon. The extension tubes afford relatively lowfrictional restraint to sliding movement of the cable 1 and if a part ofthe cable between two anchor brackets is pulled downwardly byfall-arrest forces as indicated in FIG. 2, the extension tubes of thosebrackets serve to avoid high stress concentration on the cable due tolocalised bearing contact with the metal head portions.

The following is a description of the construction of the couplingcomponent 7 as shown in FIGS. 2, 5 and 12. The component comprises alongitudinally slotted tube 20. A link 21 for connection to the worker'slanyard 8 as shown in FIGS. 1 and 2 is pivotally connected to the wallof that tube. The bore of the tube 20 is larger than the externaldiameter of the track-receiving tubular head portions 10 of the anchorbrackets so that the slotted tube can slide over those bracket headportions. The longitudinal slot 22 has over a central portion of itslength a width which is substantially smaller than the diameter of thecable 1 but is a little greater than the thickness of the neck portions11 of the anchor brackets. The opposed end portions of the slot 22 areflared so that the mouth of the slot at each end of the tube isrelatively wide. The flared portions provide cam faces or edges 23. Thelink 21 has a sleeve portion 21a (FIG. 12) which is traversed by a pivotpin 25. This pivot pin bridges an opening 26 in the wall of the tube 20.The end portions of the pin are secured in receptive holes formed inthat tube wall. The diameter of the pivot pin is such that it passesthrough the sleeve portion 21a of the link with clearance, so that thelink is very freely pivotable relative to the slotted tube. The pivotpin 25 is angularly spaced by 90° (around the axis of the slotted tube)from the longitudinal centre line of the slot 22.

As a worker moves along the walkway 3 (FIG. 1), the coupling componentis drawn along the cable 1 by the pulling force on the lanyard 8. Whenthe slotted tube reaches one of the cable anchors, first the anchorbracket extension tube 18 and then the bracket head portion 10 entersthe bore of the slotted tube. The neck portion 11 of the bracket entersthe slot 22. The coupling component therefore advances smoothly past thebracket. If the angular orientation of the slotted tube around the cable1, at the time that tube arrives at the bracket, is not such that thecentral narrow portion of the slot 22 is in alignment with the neck 11of the bracket, that neck will abut against one or another of the saidcam faces or edges 23 and thereby cause the tube 20 to turn so that thecoupling component continues its movement past the bracket without anyimpedance.

FIG. 6 shows in full line the way in which anchor brackets of the formshown in FIGS. 2-5 are orientated in relation to the overhead fixture inthe system depicted in FIG. 1. FIG. 6 shows in broken line a way inwhich the brackets can be arranged for anchoring a safety track to avertical surface. When the coupling component 7 is being drawn along thecable 1 by a pulling force on the worker's lanyard 8, the angularorientation of the slotted tube 20 around the cable will be such thatthe slot 22 is disposed to one side of the cable. The slot must be tothe same side of the cable as the neck portions 11 of the brackets.Provided that condition is satisfied, the coupling component will travelsmoothly past the brackets as previously described. As is apparent fromFIG. 6, that condition is satisfied in both of the illustrated bracketmounting positions. For suiting the anchor bracket position shown inbroken line, in which the neck portion of the bracket is on the lefthand side of the cable in the aspect of the drawing, the couplingcomponent 7 is fitted on the cable, at the time when the system isinstalled, in an orientation which is the end-for-end reversal of thatwhich suits the bracket position shown in full line.

Safety apparatus incorporating a coupling component of the form shown inFIGS. 2, 5 and 12 is described and claimed in International PatentApplication PCT/GB92/00916 in which the United States of America is adesignated state.

Anchor brackets as described with reference to FIGS. 3 and 4 wereindividually subjected to the Yield Test as hereinbefore set out. Eachbracket was formed from a 16 SWG strip of austenitic stainless steel.The strip had a width of 60 mm. Each bracket had the followingdimensions (referring to FIG. 3):

    ______________________________________                                        Vertical height from the centre of the head                                                            67 mm                                                portion 10 to the base 12:                                                    Horizontal distance from a vertical plane                                                              67 mm                                                through the centre of the head portion                                        to the outer face of side 13:                                                 Height of side 13:       54 mm                                                Overall length (measured in the plane of the                                                           60 mm                                                drawing) of the base 12:                                                      External diameter of the head portion:                                                                 18 mm                                                Diameter of apertures 14,15                                                                            13 mm                                                Diameter of apertures 16,17:                                                                           30 mm                                                ______________________________________                                    

In a first test one of the brackets was secured to a fixture with side12 (FIG. 3) of the bracket against the fixture in the same way as thebracket shown in full line in FIG. 6. A rigid bar was inserted throughthe head portion 10 of the bracket and traction force was exerted on thebracket by the traction machine via that bar. The traction force wasexerted in a direction normal to the fixture surface against which thebracket was secured. Substantial plastic deformation of the bracketoccurred before the traction force reached 2 KN. FIG. 7a represents theshape into which the bracket had become permanently deformed by thetraction force when it reached 2.5 KN. At that stage the displacement ofthe head portion of the bracket from its original position (measuredparallel with the direction of the tractive force) had reached 2 cm. Thetraction force was further increased, at the same rate, to determine theultimate tensile strength of the bracket. That ultimate tensile strengthwas found to be 49.24 KN. At that loading the metal strip fractured atthe location of the anchor bolt. Before breakage, the entire metal striphad become deformed into a single loop as depicted in FIG. 7b.

In a further test, an identical bracket was secured to a fixture withside 13 (FIG. 3) of the bracket against the fixture in the same way asthe bracket shown in broken line in FIG. 6. The test was carried out inthe same manner as the previous one except that in this case thetraction force was exerted parallel with side 13 of the bracket and in adirection towards the plane of side 12 thereof. In this test also,substantial permanent plastic deformation of the bracket occurred beforethe traction force reached 2 KN. At the stage the traction forcedreached 2.5 KN the head portion of the bracket had become permanentlydisplaced from its original position by a distance (measured parallelwith the direction of the traction force) of 4 cm. The ultimate tensilestrength of the bracket, determined by continuing to increase thetraction force at the same rate, was found to be 50.94 KN. At thatloading the metal strip factured at the location of the anchor bolt. Asin the preceding test, the metal strip became deformed into a singleloop before breakage occurred.

The very favourable combination of properties of the bracket: itsultimate strength, yield resistance and deformation characteristics, arecontributed to by the polygonal form of the bracket body, the presenceof single-ply corner angles at the junctions of single-ply sides 16 and17 with the double-ply fixing sides 12, 13, and the double-plyconstruction of the neck 11.

FIG. 8 shows an alternative form of anchor bracket which can be employedin a system according to the invention. The bracket comprises a tubularhead portion 25, a body portion 26 in the form of a triangular loop, anda neck portion 27 joining such head and body portions. The bracket canbe secured to a surface by an anchor bolt fitted through hole 28 in side29 of the body portion of the bracket. A hole 30 of larger diameter isprovided in the opposite wall of the body portion to allow access of atool to the anchor bolt head. The bracket has been formed from a singlestrip of metal. End portions of the strip overlap and are spot-weldedtogether to provide a double thickness of material where the anchor boltwill be located. It is a straightforward matter to select the bracketmaterial and dimensions so that the bracket combines a requisite highultimate tensile strength with a relatively low resistance to permanentdeformation under load in accordance with the requirements of theinvention.

Reference is now made to FIGS. 9 and 10 which show a safety track anchorcomprising a bracket 32 which incorporates coils, and a fastener 33. Thebracket comprises two components: a body component formed by a metalring 34, and a coiled track-supporting component 35. In FIG. 10 the ring34 has been indicated merely in broken outline so that parts of thecomponent 35 which lie within that ring can be seen.

The ring 34 is secured to a fixture by a fastener comprising a threadedmetal stud or bolt 36 which extends through a hole in the wall of thering, a nut 37, and washers 38-39.

The coiled track-supporting component 35, which has been formed bybending a strip metal blank, comprises two coils 40 locatedback-to-back, centrally of the width of the blank. One of those coils isapparent in FIG. 10. The other one lies immediately behind it in theaspect of that figure. The width of those coils (measured transverselyof the metal strip) is equal or nearly equal to the width of the metalring 34. When the track-supporting component 35 and the ring 34 areassembled, the said coils fit inside the ring. The strip portions 40aand 41a which can be seen in FIG. 9 are end portions of those coils.Abreast of the ends of each of the two coils 40 and co-axial therewithare two loops which in the assembly are located outside the metal tubeat opposite ends thereof. The two loops at one end of the component 35are visible in FIG. 9 and are denoted 42, 43. The loop which is co-axialwith loop 42 and located at the opposite end of the component is visiblein FIG. 10 and is denoted 44. Portions of the metal strip extendtangentially from the pairs of end loops and form two-ply arms 45, 46which project radially past the periphery of the ring 34 forming thebody component. Each arm terminates at its free end in a tubular headportion or eye through which a flexible safety track member 47 can bethreaded. The plies of the arms are spot-welded together and to the endsof the metal strip portions forming the external loops.

Instead of allowing direct contact of the safety track with the metaleyes, these can be made large enough to receive a tubular track guidelike the extension tube 18 shown in FIGS. 2 and 5. A single such tubecan be provided on each bracket so that the tube bridges the two arms45, 46.

The track-supporting component 35 is arcuately bodily displaceable aboutthe axis of the ring 34. When a system incorporating two-componentbrackets of this form is in use, if a pull is exerted on the safetytrack in a direction which is at an angle to the plane of the arms 45,46 of the adjacent track-supporting components, those track-supportingcomponents can in response to that pull turn bodily about the axis ofthe ring 34 so that the arms become aligned with the direction of thepull.

The two-component bracket can be used for anchoring the safety track toan overhead horizontal fixture surface as shown in FIG. 9 or to avertical fixture surface at any of a number of different levels.

The washer 38 provides a part-cylindrical seating face for the ring 34.If a load of sufficient magnitude is applied to the safety track betweentwo of the anchors, the force will exert on those anchors a turningmoment causing the anchor rings to slip on their seating faces intoangular positions, so reducing the stress concentration on the safetytrack.

Brackets of the form represented in FIGS. 9 and 10 can easily be made toachieve the required ultimate strength and yield resistance properties.Brackets of that form, made from 16 SWG austenitic stainless steel andhaving an ultimate tensile strength (as determined in a Yield Test ashereinbefore described) of about 50 KN were found to have a yieldresistance somewhat lower than that of the tested quadrilateral bracketshereinbefore described which were made from the same material and had asimilar ultimate tensile strength. During the build up of the tractionforce the ring 34 of the brackets became deformed into an elongate loop;the spot welds in the track-supporting component 35 ruptured, and theloops and coils of that component contracted with consequent extensionof the arms 45 and 46. FIG. 11 represents the form of such a bracket ata stage during the progressive increase of the traction force from 0 to5 KN.

In the event of the fall of a worker using a safety system incorporatinganchor brackets of the forms shown in FIGS. 9 and 10, the permanentdeformation of the brackets which would take place under the appliedload would make it very apparent to an inspectorate that the system hasbeen subjected to heavy loading due to a fall and would also make itvery apparent at what region of the system the fall occurred. Thedeformation of the brackets would of course also contribute to energyabsorption.

FIG. 12 shows part of a system according to the invention which exceptfor the anchor brackets is the same as that described with reference toFIGS. 1 to 5. Parts of the system corresponding with parts of the systemaccording to FIGS. 1 to 5 are denoted by the same reference numerals.Each of the brackets in the system according to FIG. 12 is formed from ametal blank which is bent to form a two-ply base flange 50, a two-plycantilever arm 51 and a track-receiving eye 52 at the free end of thatarm. It is a straightforward matter to select the material anddimensions of an anchor of that form so that it has the required highultimate tensile strength and a relatively low resistance to permanentplastic deformation as required by the invention.

We claim:
 1. A personnel fall-arrest system comprising a flexible safetytrack (1) held in spaced relation to a fixture (2) by brackets (5) whichare located at intervals along the track (1) and are secured to thefixture (2), and a coupling component (7) for connecting a worker'ssafety harness to said track via a safety line (8), said component (7)being coupled to said track but being freely displaceable therealong,each of the brackets has a head portion (10,25) which surrounds andlocates the safety track (1), a body portion (9,26) formed by a loop ofmaterial between said head portion and the fixture (2), and a neckportion (11,27) joining said head and body portions; said head (10,25),neck (11,27) and body (9,26) portions of the bracket being integralparts of a single strip of material which has been folded abouttransverse axes to define those bracket portions and so that twoportions of the strip lie face to face to form a two-ply bracket wall(12,13,29) by which the body portion of the bracket is secured to thefixture (2); said bracket having an ultimate tensile strength more thansufficient to prevent release of the track under the maximum load liableto be imposed on said bracket (5) due to the fall of a person using thesystem but having a resistance to permanent deformation such that a loadsubstantially smaller than that maximum will suffice to cause it toundergo obvious permanent deformation.
 2. A system according to claim 1,wherein each of the brackets has a resistance to permanent deformationsuch that if the bracket is subjected to a Yield Test in which aftersecuring the bracket to a fixture in the same way as it is in thefall-arrest system, a traction force is applied to the head portion ofthe bracket by means of a traction machine working at an extension rateof 0.5 inches (1.27 cm) per minute so as to subject the bracket to afinal traction force of 3 KN in a the direction in which it would beloaded in the event of the fall of a person using the system, that forcecauses the head portion of the bracket to be displaced from its originalposition by a distance, measured in the direction in which the force isapplied, of at least 2 cm.
 3. A personnel fall-arrest system comprisinga flexible safety track (1) held in spaced relation to a fixture (2) bybracket (5,32) which are located at intervals along the track (1) andsaid brackets are secured to the fixture, a coupling component (7) forconnecting a worker's safety harness to said safety track via a safetyline (8), said coupling component (7) being coupled to said safety trackbut being freely displaceable therealong, each of the brackets beingformed by folding a metal strip so that the bracket has a tubular headportion (10,25,52) which locates and slidably supports the safety track(1) and a body portion (9,26,34) in the form of a loop having a wallportion (12,13,29) which is formed by overlapping end portions of saidmetal strip and by which the wall portion of the bracket is secured tothe fixture, said bracket having an ultimate tensile strength more thansufficient to prevent release of the track under the maximum load liableto be imposed on it in the event of the fall of a person using thesystem but having a resistance to permanent deformation such that a loadsubstantially smaller than that maximum will suffice to cause it toundergo obvious permanent deformation.
 4. A system according to claim 3,wherein each of said brackets (5) has a body portion (9,26) which is inthe form of a polygonal loop, and has a neck portion (11,27) whichprojects from one corner of the polygonal loop and said neck portionjoins that body portion to the head portion (10,25) of the bracket.
 5. Asystem according to claim 3, wherein each of the brackets has aresistance to permanent deformation such that if the bracket issubjected to a Yield Test in which after securing the bracket to afixture in the same way as it is in the fall-arrest system, a tractionforce is applied to the head portion of the bracket by means of atraction machine working at an extension rate of 0.5 inches (1.27 cm)per minute so as to subject the bracket to a traction force of 3 KN inthe direction in which it would be loaded in the event of the fall of aperson using the system, that force causes the track-holding portion ofthe bracket to be displaced from its original position by a distance,measured in the direction in which the force is applied, of at least 2cm.